800℃长期氧化过程中含铝奥氏体耐热钢中第二相的演化规律

摘要

采用真空电弧熔炼技术制备了含铝奥氏体耐热钢，经过冷轧和热处理后，研究了其在800℃含10％(体积分数)水蒸气的空气中氧化100~7200 h 过程中第二相的演化规律。结果表明：氧化前试验钢中基本没有第二相析出，而氧化后在奥氏体基体中主要析出了 NbC、Laves-Fe2 Nb、B2-NiAl和σ-FeCr四种第二相；细小的NbC呈弥散分布，随着氧化时间的延长其数量和形态无明显变化；奥氏体晶界上析出的 B2-NiAl 相随着氧化时间的延长不断粗化且呈不连续分布，而晶内的主要以细小的短棒状弥散分布；氧化层与奥氏体基体间出现明显的 B2-NiAl 贫化区，其宽度随氧化时间的延长而不断增加；σ-FeCr 相不连续地分布在奥氏体晶界上，并随着氧化的进行而不断粗化。%An alumina-forming austenitic heat-resistant steel was produced by the vacuum arc melting technique.After cold-rolling and heat treatment,the evolution of secondary phases in the steel was investigated during the process of oxidation at 800 ℃ for 100-7 200 h in the air containing 10vol% water vapor.The results show that before oxidation no second phases in the tested steel were precipitated.However,four second phases of NbC,Laves-Fe2 Nb,B2-NiAl andσ-FeCr were found in the austenitic matrix after oxidation.The fine NbC phase showed a dispersive distribution and the amount and shape remained unchanged with the increase of oxidation time. With the increase of oxidation time,the B2-NiAl phase on the austenitic grain boundaries was coarsened and dispersed discontinuously while that in austenitic grains was dispersed well with a fine and short-rod-like shape. Between the oxide scale and the austenitic matrix,the obvious NiAl denuded zone appeared and whose width increased with the oxidation time increasing.Theσ-FeCr phase was discontinuously distributed on the austenitic grain boundaries and coarsened with the oxidation continuing.